1. Field of the Invention
This invention relates to water cooling towers and especially an improved film fill assembly for use in an evaporative type cooling tower.
In particular, the invention is concerned with a film fill assembly made of packs of fill sheets arranged in vertically oriented, side-by-side relationship. The individual sheets are each formed to present not only a chevron-patterned central air-water contact zone, but also to define corrugated upper marginal sections which mutually cooperate with the same sections of adjacent sheets to provide for even distribution of hot water over the plan area of the fill assembly. Each of the sheets is further provided with partial honeycomb side marginal portions which are mutually cooperable in an assembled fill pack to define passages which control the path of inflowing or outflowing cooling air or the flow of air between horizontally aligned packs. An integral horizontally extending corrugated section may be provided if desired between the upper and lower edges of each sheet to effect redistribution of the hot water as it flows downwardly over the main air-water contact zone of respective fill sheets.
The unique shape of the film fill sheets not only permits fabrication of the individual sheets using conventional vacuum forming techniques, but also allows minimization of the number of different types of sheets which must be formed and thereafter assembled to present a pack which retains required thermal performance characteristics without untoward air pressure drop.
2. Description of the Prior Art
Water cooling tower fill assemblies for many years typically were made up of a series of horizontally oriented, flat splash bars located in horizontal and vertically spaced relationship in disposition such that hot water gravitating through the fill impacted on the bars and was broken up into droplets to increase the surface area of the water and thereby increase cooling efficiency.
In recent years, film fill packs made up of vertically positioned, horizontally spaced synthetic resin sheets have replaced the splash bars because of the flame retardant nature of such materials, the decreased size of the overall fill assembly thus lowering pumping heights, and minimization of the overall size of towers incorporating film fill units.
Film fill design parameters include the requirements of spreading the water out over the surface of the fill sheets in a thin film for maximum surface area, retarding of the gravitational flow of the water to the extent feasible to assure maximum exposure of the water to cooling air, and providing turbulent airflow without excessive air pressure drop.
To these ends, each face of sheet fill members forming multiple-sheet fill assemblies are often formed with sets of zig-zag chevron patterns which effectively increase the available surface area of the fill and decrease the velocity of flow of the descending films of water. The chevron pattern also lends itself to being produced by conventional vacuum-forming techniques, long employed in the plastics industry. During the vacuum-forming process, selected areas of the initially flat, synthetic resinous sheet are subjected to negative pressures to draw the areas into cavities of a forming die, thereby creating the desired pattern of peaks and valleys on one face of the sheet which each define a respective valley and peak on the opposite face of the sheet. In this regard, exemplary chevron pattern film fill sheets are depicted and described in U.S. Pat. Nos. 3,733,063, 4,320,073 and 4,548,766, all of which are assigned to the assignee of the present application.
Moreover, it is highly important to maintain the required spatial relationship between the chevron-patterned cooling zones of adjacent sheets of the fill assembly in order to avoid development of undue localized air pressure drops which can significantly decrease the thermal performance of the film fill. During operation of a cooling tower, it has been found that when thin synthetic resin sheets assembled into a fill are loaded with hot water, the sheets sometimes have a tendency to warp, bend or buckle thus reducing the cross-sectional area of the adjacent space available for passage of air. Additionally, because the relatively thin sheets are normally fashioned of a thermoplastic such as polyvinyl chloride, the sheets have an increased tendency to sag and warp under the normal operating conditions of the cooling tower.
At the top of the fill pack, marginal top edge portions of sheets also tend to deflect toward each other on a random basis thus precluding equal distribution of hot water across the full plan area of the film fill assembly and hindering uniform gravitational flow of water downwardly across opposed faces of each sheet of the fill pack.
In the past, integral, individual spacers have often been formed in the film fill sheets in an effort to maintain uniform spacing of the sheets throughout the pack. One example of such spacers is shown in the aformentioned U.S. Pat. No. 4,320,073 wherein outwardly extending indexing units are disposed at spaced locations throughout the chevron-shaped cooling zones of the sheet member for engagement with respective recess-defining walls located on the next adjacent sheet. While such indexing units have been found to be satisfactory when present in sufficient numbers for maintaining the desired spacing between adjacent sheets in areas within the chevron-patterned cooling zones, the spaced, integral indexing units of the cooling zones cannot be relied upon to entirely prevent warpage of top marginal edge portions of each sheet. Furthermore, if an adequate number of the spacers is provided to insure against deflection of the fill sheets, the spacers represent an impedence to airflow which alters the thermal performance of the fill pack.
For the most part, film fill assemblies have been used in small package-type water cooling towers. Recently, however, more and more emphasis has been placed on adapting such film fill assemblies for use in larger, industrial-type water cooling towers. However, the characteristics and construction of conventional vacuum forming machines limit for practical purposes the width of each sheet which may be formed on such equipment. Typically, this is a dimension of no more than about four feet. As a result, two packs of fill members are often arranged in side-by-side relationship in the direction of airflow to present a fill assembly which is of adequate dimensions between the air inlet and the air outlet. The outwardmost edge portions of the outboard fill pack sheets are normally formed to present an upright series of air inlet louvers, while the marginal, innermost edge portions of the inboard fill pack may be formed to present drift eliminator structure for separating entrained water droplets from the currents of air flowing out of the fill assembly.
Although these inclined air inlet louvers and drift eliminator components presenting air inlet and air outlet passages are of convoluted shape which prevents for the most part substantial deflection and warpage of the upright outermost edge portions of the fill sheets under normal hot water temperature conditions, the same has not been the case as to the upright edges of the fill packs which are in directly abutting, proximal relationship. However, there is also a significant need to preclude warpage and deflection of the edge portions of the fill packs which are in abutting relationship since uniform transfer of air from the outboard fill pack into the inboard fill pack is essential for maximum thermal performance efficiency.
Finally, it has often been necessary to provide a deck assembly or other water distribution structure in direct overlying relationship to the upper faces of the film fill packs underneath the hot water distribution deck or distributor apparatus in order to assure uniform loading of water across the entire plan area of the fill. Even with the attendant extra expense incurred by the provision of distribution structure overlying the film fill packs, the incorporation of such added equipment often has not resolved the problem because of warpage and deflection of the upper edges of the film fill sheets thus preventing the water from flowing in substantially equal proportional amounts into all of the spaces between proximal fill sheets rather than channeling into certain of the passages depending upon the actual extent of the open areas presented at the top of the film fill packs.